1. Field of the Invention
The present invention relates to a variable valve apparatus of an internal combustion engine, which varies the phase of an intake valve or an exhaust valve.
2. Description of the Related Art
Many reciprocating engines mounted in automobiles include a variable valve apparatus for changing the phases of an intake valve and an exhaust valve, for reasons of engine gas emission countermeasures, fuel consumption reduction and the like.
Many of such variable valve apparatuses employ a structure in which the phase of a cam formed on a camshaft is replaced with an oscillating cam in which a base circular zone and a lift zone are ranging. Specifically, a structure is employed in which an oscillating range of the oscillating cam is changed, whereby a valve opening period and a valve lift amount of the intake valve and the exhaust valve driven via a rocker arm are varied continuously.
In order to improve a pumping loss, a structure is proposed in Jpn. Pat. Appln. KOKAI Publication No. 2003-239712 in which a transmission arm is interposed between a cam and an oscillating cam, and the transmission arm is oscillatably supported by a control shaft.
Specifically, the transmission arm is moved by the turning displacement of the control shaft. A contact position of transmission arm and the cam is changed by moving the transmission arm. By changing the contact position of the transmission arm and the cam, the valve characteristics, that is, a valve opening period, valve open-close timing and a valve lift volume are continuously varied.
In such a variable valve apparatus, it is known that, when an engine is operated at a high valve lift and at a high speed, a force for driving an intake valve or an exhaust valve becomes large by a positive acceleration zone of a cam lift just after opening the valve and just before closing the valve.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-239712, in most variable valve apparatuses using a transmission arm, a valve driving force at opening the valve, and a reaction force working onto a contact point portion of an oscillating cam and a contact point portion of a cam at closing the valve are applied to an oscillating fulcrum of the transmission arm in a same direction at the high valve lift and high speed operation.
In the structure in which the resultant force of these forces works on the oscillating fulcrum, a load amount to be added is large. Therefore, when the force for driving the valve becomes large and the like, an excessive load is likely to work on the oscillating fulcrum of the transmission arm.
In particular, when an excessive load works on the control shaft, there occurs a deformation under torsion in the control shaft. Therefore, there is a fear that preset valve characteristics, that is, valve lift amount and the like may not be reproduced. Further, an actuator having a large capacity and a large size enough to generate a torque to overcome an excessive torque is required.
In particular, in the case of a multicylinder engine in which valve characteristics of each cylinder are varied by a common control shaft, the influence of the deformation under torsion of the control shaft tends to become larger in the cylinders away from the actuator in comparison with the cylinders near the actuator that turns the control shaft.
Therefore, in the multicylinder engines, there occur differences in the valve lift amount and the valve opening period among the cylinders, and there occur differences in the combustion conditions among the cylinders, which causes vibration in the engine, degrades the output, and degrades the fuel consumption.
Under such circumferences, in these variable valve apparatuses, countermeasures must be taken by use of a strong oscillating fulcrum durable to an excessive load and a highly rigid control shaft.
However, these countermeasures make the structure of the variable valve apparatus complicated, and additionally make the structure around the control shaft including the control shaft large.